Light signal apparatus

ABSTRACT

A pair of oppositely directed beams of light are rotated about an axis. The direction of the beams has a small deviation from a plane normal to the axis, whereby flashes of equal strength from both beams are produced in the normal plane at twice the frequency of revolution, thereby indicating the normal plane to a viewer. In similar manner, a line may be indicated by making a beam rotate about an axis having a small deviation from that of the beam.

04-l8-72 XR 3,656,828

United States ratem [151 3,656,828 Scholdstrom [4 Apr. 18, 1972 54] LIGHT SIGNAL APPARATUS 3,170,982 2/1965 Hemstreet et al .350/102 72] Inventor: Karl Ono Ragnar Scholdstmm Lidingo, 3,426,144 2/1969 Roth .350/7 ux Sweden Primary Examiner-David Schonberg [73] Assignee: AGA Aktiebolag, Lidingo, Sweden Assistant Examiner-Michael J. Tokar [22] Filed, D e c 17 1969 Attorney-Larson, Taylor and Hinds [21] Appl. No.: 885,799 [57] ABSTRACT A pair of oppositely directed beams of light are rotated about Forelg" Application Dam an axis. The direction of the beams has a small deviation from Jan. 24, 1969 Sweden ..934/69 a Plane normal M119 axis, whereby flashes of equal Strength from both beams are produced in the normal plane at twice [52] U.S. Cl ..350/7, 356/138, 356/153, the frequency of revolu i thereby n i ing he normal 356/172 plane to a viewer. {g In similar manner, a line may be indicated by making a beam 3 rotate about an axis having a small deviation from that of the l 1 7 7 7 [56] References Cited UNITED STATES PATENTS 4 Claims, 2 Drawing Figures 2,997,598 8/1961 Gramm ..350/7 PATENTEDAPR 18 m2 3, 656,828

INVl-INTOR KARL 0.R. SCH'O'LDSTRO'MI 1.10m SIGNAL APPARATUS BACKGROUND OF THE INVENTION the two signals are of equal strength. For instance,-the listener I may hear the Morse code signal N in one beam and A in the other and a continuous tone in the region of equal strength.

SUMMARY OF THE INVENTION The present invention implies a modification of the known principle adapted for the human eye. According to the invention a light emitter is provided for generating a beam of visible light having a portion of highest intensity. Means are provided for scanning the portion of highest intensity of the beam-over an adjacent region to the spatial region to be defined symmetrically with regard thereto. The spatial region to be indicated can then be distinguished by the eye from the adjacent region, within which there is a lower intensity of the, light. .Owing to the symmetrical scanning, this lower intensity, which may be represented by a total absence of light, is surrounded by a higher light intensity and can easily be discerned. In a preferred embodiment of the invention, light-pulses'of substantially lower frequency are produced within the. adjacent region than in the region to be indicated, so that the observer will see a continuous light within the latter :and a more pronounced flicker the farther he moves out of it. This principle can be used owing to the well-known slowness of response or threshold frequency of the human eye.

THE DRAWING FIG. 1 is a schematic diagram of an embodiment of the invention for indicating a plane, and

FIG. 2 is a detail view of a modified embodimentfor indicating a line.

DESCRIPTION OF EMBODIMENTS In FIG. 1, LE designates a light emitter for producing a beam of light B. The emitter comprises a laser light source LS generating a beam of nearly parallel light which is passed through a beam expander BE. A typical 'value of divergence for a laser beam is l mR (1 m/km) and of the beam diameter 1 mm. The expander BE is of a type well known within the art comprising a combination of a negative and a positive lens and transforms the beam into one having, for instance, a divergence of 0.1 mR and a diameter of mm. This facilitates the subsequent splitting of the beam. Otherwise, the expander is not necessary, and it may even be preferable not to use one in some instances, since the moredivergent beam is easier to find. A means for orienting the apparatus is shown in the form of a level MO. A similar level may be provided at right angles to the one shown, permitting the emitted beam to be adjusted to have its axis A accurately vertical. Adjustable supports of well-known type may be provided on the instrument for this purpose and are not shown, as they form no part of the present invention.

A laser beam, as is well known, has a portion of highest intensity in the vicinity of the center thereof.

The apparatus also comprises means MS for scanning the portion of highest intensity of the beam over a region R, R, which is adjacent and symmetrical relative to the spatial region R to be indicated. The scanning means MS comprises a deflecting means DM in the form ofa prism having a rectangular edge which cuts the beam B at the center thereof and one revolution, one flash being produced by the-half-beam B which-has a slight inclination relative tothe axis A. The beam '3 'isthus-split into two half-beams. One of these is designated 8' and 'is represented as a lobe which is'symr'netrical about a line R. The origin of "the lobe is at the intersection ofthe line R with'the reflecting surface ofthe prism DM and'the'length of. the radius-vectorfromthe intersection to a point'of the lobe representsthe strength of the. light'in'the direction of the .vec-

torl Thedistribution is seen tocorrespond'to a highest'intensity of the beam in the centralposition thereof.

"Theprism DM is held in a'support SU which is attached to the shaft SH of amotor M, whichserves to rotate the prism. The shaft SH is coaxial withthe axisA.

The second half-beam B is directed opposite to the halfbeam B.-The second half-beam B is also shown in dashed lines on the drawing inthe position B which it will take after oneshalf revolution ofthe prism DM about the axis A.

Thespatial region to be indicated is the horizontal plane corresponding to'the line R. To the eye of an observer, if located in this plane, aflash of light will appear-twice during in the position shown on the drawing and the other being produced bythe half-beam B one half-tum later. On the other hand, if'the eye is in the direction'R or R, it will seeonly one of the half-beams, which-will appear once for each' revolution.

As a result of this, therefore, light flashes are produced in the direction R with afrequency of 2f and in the direction of R or R with the frequency f, if f is the number of revolutions per minute of the motor M.

1 At a point between R and R, both light flashes will 'be present, however the strength of the flash from the half-beam B is stronger than that from B. By a suitable choice of' the angle between R and R" it is possible to achieve a great difference in strength between the two beams even for a small deviation of the eye from the direction R.

It is clear that the FIG. 1' apparatus can easily be modified for indicating a plane of adjustable inclination with the aid of graduated circles and bearings for adjustably supporting the apparatus, thereby enabling adjustment of the inclination of the axis of rotation A.

The frequency f may have a value such as 20cps, which will cause the frequency 2f to appear as continuous light tothe eye of the observer.

FIG. 2 is a detail view of a modified embodiment for indicating a'line. The beam B is emitted with its axis A directed along the line to be indicated and a wedge DM is placed with its plane of symmetry perpendicular to the axis A and rotatable about it, whereby the axis A of the deflected beam will generate a conical surface and an eye which is placed in the direction A will see one flash for each revolution of the wedge. To an eye placed in the direction A, however, the light will appear continuous, if the beam is symmetrical about its axis of rotation A.

I claim:

1. A light signal apparatus for visibly indicating a spatial plane, comprising: a light emitter for generating a beam of light and scanning means comprising optical deflecting means for receiving said beam and producing first and second beams substantially orthogonal to said beam and means for rotating said optical deflecting means to provide scanning of said first and second beams, said optical deflecting means including means for causing scanning of the highest intensity portion of the first beam within a small angle with respect to said spatial plane so that a relatively low intensity portion of said first beam is scanned through the said spatial plane and for causing scanning of the highest intensity portion of the second beam within a small angle with respect to the said spatial plane and on the opposite side of said spatial plane from the angle through which the first beam is scanned so that a relatively low intensity portion of said second beam is scanned through the said spatial plane, said first and second planes being located symmetrically relative to said spatial plane and said relatively low intensity portion of said first beam overlapping said relatively low intensity portion of said second beam.

2. A light signal apparatus as claimed in claim 1 in which plane at a first frequency and said adjacent planes at a second, said optical deflecting means comprises an ofiset prism for lower frequency. splitting said light beam into said first and second beams and A llght 518ml apparatus as clalmed clalm 3, Whlch for directing said first and second beams in opposite Said first q lf is above the threshold qP y of the di i 5 human eye and said second, lower frequency below the 3. A light signal apparatus as claimed in claim 1, in which threshold frequency of the human said scanning means comprises means for scanning said spatial 

1. A light signal apparatus for visibly indicating a spatial plane, comprising: a light emitter for generating a beam of light and scanning means comprising optical deflecting means for receiving said beam and producing first and second beams substantially orthogonal to said beam and means for rotating said optical deflecting means to provide scanning of said first and second beams, said optical deflecting means including means for causing scanning of the highest intensity portion of the first beam within a small angle with respect to said spatial plane so that a relatively low intensity portion of said first beam is scanned through the said spatial plane and for causing scanning of the highest intensity portion of the second beam within a small angle with respect to the said spatial plane and on the opposite side of said spatial plane from the angle through which the first beam is scanned so that a relatively low intensity portion of said second beam is scanned through the said spatial plane, said first and second planes being located symmetrically relative to said spatial plane and said relatively low intensity portion of said first beam overlapping said relatively low intensity portion of said second beam.
 2. A light signal apparatus as claimed in claim 1 in which said optical deflecting means comprises an offset prism for splitting said light beam into said first and second beams and for directing said first and second beams in opposite directions.
 3. A light signal apparatus as claimed in claim 1, in which said scanning means comprises means for scanning said spatial plane at a first frequency and said adjacent planes at a second, lower frequency.
 4. A light signal apparatus as claimed in claim 3, in which said first frequency is above the threshold frequency of the human eye and said second, lower frequency is below the threshold frequency of the human eye. 